Exposure to stress elicits behavioral and physiological responses in animals and humans, including changes in food intake and body weight. This proposal will take advantage of a unique animal model of social stress, the Visible Burrow System (VBS). The VBS provides a semi-naturalistic environment in which a dominance hierarchy naturally develops among male rats producing dominant (DOM) and subordinate (SUB) animals that can be easily identified with minimal experimenter intervention. Although significant changes in body weight among the SUB group have been reliably observed, little if anything is known of its etiology. In addition, the long-term consequences of altered body weight regulation resulting from chronic social stress have not been examined in this model. The proposed experiments will lay the groundwork for understanding these and other stress-related conditions in humans and may point to novel therapeutic strategies. The specific aims are: 1) to test the hypothesis that body weight loss in subordinates during VBS housing is attributable to decreased food intake and/or to increases in energy expenditure, 2) to test the hypothesis that physiological, endocrine and neurochemical changes that are evident following 14 days of chronic stress in the VBS will return to control levels when the animals are allowed to recover outside the VBS. A secondary hypothesis is that SUB will gain weight during recovery preferentially as adipose tissue and DOM will gain weight primarily as lean body mass, 3) to test the hypothesis that multiple, intermittent episodes of social stress produce more severe and enduring changes of brain neurochemistry and energy homeostasis than a single episode.